In recent years, with the rapid development of the petrochemical industry, water resource shortage has become a principle factor restricting China's economic and social development. Therefore, the water resource utilization has drawn more and more attention. Reverse osmosis not only can effectively remove inorganic salt ions in water, but also can remove colloids, bacteria, viruses, bacterial endotoxin and most of impurities such as organics and the like in water. Moreover, reverse osmosis has high system stability and low operating cost. Therefore, reverse osmosis becomes a main technical means for recycle of reclaimed water. However, after the reverse osmosis treatment, in addition to the water that can be reused, reverse osmosis concentrated water which is concentrated for 3-5 times (relative to the reclaimed water before the reverse osmosis) can be produced. The obtained reverse osmosis concentrated water has the following defects: higher dissolved organics content, high solution chromaticity, high salt content, and poor biodegradability.
The conventional treating methods of reverse osmosis concentrated water containing high COD use ozone, hydrogen peroxide and the like as an oxidant. It is oxidized under the action of catalyst, ultrasound and the like to degrade organics so as to meet the emission standards. CN 102040294 A discloses a method for treating reverse osmosis concentrated water by ozone and hydrogen peroxide as an oxidant with activated carbon adsorption, its oxidant dosage is large, and the running cost is relatively higher. CN 102153171 A discloses a method for treating reverse osmosis concentrated water by ozone catalytic oxidation, which causes secondary pollution due to aeration during the process, in which the offgas needs to be treated. CN 102633410 A discloses a method for treating reverse osmosis concentrated water by photocatalytic oxidation combined with biochemistry. Since the process thereof contains biochemistry, it is only suitable for reverse osmosis concentrated water with a lower salt content, and the effect of photocatalytic oxidation and biochemically reducing COD is poor, and it is not suitable for reverse osmosis concentrated water with higher COD. CN 103449635 A discloses a method of treating reverse osmosis concentrated water by Fenton oxidation process. The defects of the method lie in that Fenton oxidation process needs to be conducted under an acidic condition, pH needs to be adjusted in the process, a large amount of precipitation is produced in the process, and the treatment cost is high.
CN 102849879 A discloses a method for recovering part of water by electrodialysis after pre-treatment of reverse osmosis concentrated water, but no specific solution is provided for how to treat concentrated water produced by electrodialysis. CN 103723799 A and CN 104445788 A disclose that the reverse osmosis concentrated water is further processed by a combined process of ultrafiltration and reverse osmosis, and part of the water is recovered, the produced concentrated water is deeply concentrated by electrodialysis, and the fresh water produced in the concentration process is reused, the concentrated water is evaporated and crystallized. CN 104609610 A discloses that a reverse osmosis apparatus is used to recover part amount of water. The concentrated water is further concentrated by forward osmosis. The water produced by forward osmosis is reused, and the remaining trace amount of concentrated water is fed into an evaporation apparatus for treatment, and the purpose of zero discharge is finally achieved. The advantages of the above schemes lie in that reverse osmosis concentrated water is further recycled after treatment, so that the overall utilization rate of water is improved. However, no matter which one of the reverse osmosis, electrodialysis, and forward osmosis and the like is used, concentrated water with an extremely high salt concentration (salt content is 15-18 wt %) is produced, and further treatment by evaporation and crystallization is required. Due to the high salt content, the crystallizer is basically made of titanium, which requires high investments and operation costs. Multi-effect evaporation and mechanical vapor recompression (MVR) are two common evaporation crystallization techniques. Calculated on high-salt wastewater of 10 t/h, the multi-effect evaporation technology needs an investment of CNY 3 to 5 million and an operating cost of CNY 60-70 per ton; the MVR technology needs an investment of CNY 8-12 million and an operation cost of CNY 35-45 per ton. In view of the above, the bottleneck for widespread use of a near zero emission process for reverse osmosis concentrated water lies in the treatment of the high salt concentrated water which is obtained after desalination treatment and difficult to be treated. Therefore, it is necessary to develop a highly efficient and economical near zero emission process of reverse osmosis concentrated water.